Summary of the invention
The objective of the invention is for solving the assignment problem of STBC scheme downlink transmission power, just the selection problem of descending transmitting antenna.Since the distributed channel mid power and etc. the STBC that sends of speed very uneconomical, must carry out the adjustment of transmitted power.Propose to be suitable for the power distribution method of descending STBC scheme in the DWCS for this reason, have good performance and practicality.
The invention is characterized in,, contain following steps successively for a single user's DWCS:
Step (1), setting transmitting terminal has n foundation station antenna, and this n root antenna is divided into l bunch that scatters in the space arbitrarily, and j bunch antenna number is q
j, j=1,2 ... l; The user antenna of receiving terminal has the m root; Have independently between every antenna of transmitting terminal and central processing unit that cable is connected, handle the signal that sends and receive by this central processing unit;
Selected central processing unit adopts the send mode of Space-Time Block Coding, send at transmitting antenna constant power with cluster inside, and in the transmitting antenna that combines by any cluster of antennas at the set, between different bunches, carry out according to the following steps, make the outage probability minimum of system;
Step (2), receiving terminal are estimated the decline correlation matrix R of n * n transmitting antenna according to reception pilot signal and all available transmit antenna
t, m * m reception antenna decline correlation matrix R
r
Described R
t=diag (α
1R
T, 1... α
LR
T, L), R wherein
T, jRepresent q
j* q
jJ bunch normalization transmitting antenna correlation matrix, α
jBe j bunch large scale decline information, the R of required estimation
T, jCharacteristic value be λ
J, k=1 ... K
j,, K wherein
jBe the number of j bunch of characteristic value,
Described R
r=E{HH
H}/n, H are channel matrix, R
rBe that a diagonal element is 1 multiple symmetrical square, this R
rK characteristic value λ arranged
iExpression, i=1 ... K;
Step (3), the central processing unit of transmitting terminal is according to each characteristic value from the receiving terminal feedback, for all transmitting antenna set, the method for coming equal proportion ground to distribute power by the order of each bunch transmitting antenna correlation matrix between each bunch of each transmitting antenna set is with following formula set of computations A
iThe expression formula of the average error sign ratio when transmitting MQAM and MPSK symbol:
Coefficient q
J, k, i, uFor
Wherein, as noise variance σ
2=1 o'clock, ρ was an average transmitting power and the ratio of receiving terminal noise power.α
jRepresent j bunch large scale decline information, j=1 ... l, λ
J, k=1 ... K
j, be the correlation matrix R of j bunch of transmitting antenna
T, jK
jIndividual different characteristic value, λ
J, kTuple be τ
J, k, satisfy
R just
T, jOrder be t
j, 1≤t
j≤ q
j, λ
i, i=1 ... K is the correlation matrix R of normalization reception antenna
rK different characteristic value, λ
iTuple be τ
i, satisfy
That is to say R
rOrder be m
1(1≤m
1≤ m),
J=1 ..., l, beta, gamma, ζ are subscript,
Be the Appell hypergeometric function,
Be hypergeometric function, (a)
n=Γ (a+n)/Γ (a),
And
Be the Gamma function.
Step (4), this central processing unit be the average error sign ratio of all transmitting antenna set relatively, seeks its minimum value, thereby determines required antenna set and power division.
For the downlink transfer of STBC scheme in the sub-clustering DWCS, method proposed by the invention is to utilize the channel information (sending and receive the characteristic value of correlation matrix) of large scale to carry out the optimized distribution of transmitted power at transmitting terminal.This power allocation scheme based on large-scale channel information has been considered the average influence of small scale decline, has only after large scale information changes, and transmitting terminal just can be adjusted accordingly.After transmitting terminal is known whole channel informations, can select accordingly equally, the feedback that is whole channel informations can cause very big expense, and computational complexity is very high, is very unpractical method.
The method utilization large scale information seldom that the present invention proposes, carry out optimized distribution of power at transmitting terminal, obtained simple and effective suboptimum power allocation scheme, that is exactly: for the antenna set of optimum, the proportional distribution power of order according to the transmission correlation matrix of every bunch of antenna, in conjunction with a day line options, just can be near the performance of optimum, thus successfully solved the problem of power division very crucial when STBC transmits in DWCS.Compare with the scheme of the whole antenna transmission of constant power, performance is greatly improved, because this programme computing is simple, is very suitable for adopting in practice again.
Embodiment
The distribution method that is suitable for the downlink transmission power of Space-Time Block Coding in the DWCS that the present invention proposes is characterized in that for a single user's DWCS, antenna for base station has the n root, and user antenna has the m root.N root antenna is divided into l bunch that scatters in the space arbitrarily, and j bunch (j=1 ..., antenna number l) is q
jThe transmitting antenna of supposing different bunch inside exist to a certain degree correlation, and also there is correlation in reception antenna.Adopt the delivery plan STBC of Space-Time Block Coding.Sending with the inner constant power of cluster, between different bunches then at transmitting terminal according to carrying out power division from the receiving terminal feedack, make the average SER minimum of system.
The purpose that the transmitting terminal that the present invention proposes carries out power division is to make STBC scheme average SER minimum of system during downlink transfer in DWCS, with the transmission that realizes optimizing.
Consider the most general antenna model: (n, l, q
1..., q
l, m) antenna structure.As shown in Figure 1, suppose to have n root transmitting antenna and m root reception antenna, n root antenna is divided into l bunch that scatters in the space arbitrarily, and j bunch antenna number is q
jEach antenna has all independently with processing center that cable is connected, and handles the signal that sends and receive.Because each bunch spaced antenna spatially scatters, its spacing is far longer than signal wavelength, does not have correlation between spaced antenna.The antenna of each bunch inside and reception antenna are concentrated and are placed, and therefore may have correlation to a certain degree, and correlation is owing to less spacing or transmission environment between antenna causes.Because the user is possible different apart from length to the access of each spaced antenna, make that path attenuation differs greatly between each bunch, it is independent separately to add the shade large scale decline that different access path experiences, therefore, experienced different large scale declines (path fading, shadow fading) from the signal of each bunch spaced antenna transmitting-receiving.
The bandwidth of supposing channel is 1Hz.Before sending, at first to carry out the selection of antenna set, the Space Time Coding device produces the symbol that average energy is 1 empty time-code then, and the power weightings of passing through power division matrix P again sends in the antenna set of selecting at last.Through channel, the baseband signal of reception can be expressed as
Wherein x is that a n * 1 sends vector, and its j component representative is by the transmission signal of j root transmitting antenna.Y is that a m * 1 receives vector, and its i component represented the received signal of i root reception antenna.N is a m * 1 additivity white complex gaussian noise vector, and its each component is the wide Gaussian random process of steadily answering of independent same distribution, and its average is 0, and variance is σ
2ρ is total average transmitting power in the symbol period, because supposition noise variance σ
2=1, so can represent the ratio of average transmitting power and receiving terminal noise power with ρ, (being expressed as TSNR, transmit signal to noise ratio).TSNR is general bigger, because the decline of the large scale between will overcoming from the transmitting antenna to the reception antenna.
Channel matrix H can be expressed as R
r 1/2H
wR
t 1/2, H
wAll elements independent and with distributing, obey the multiple Gaussian Profile of 0 average unit variance, i.e. [H
w]
Xy~Norm (0,1/2)+Norm (0,1/2) j.R
tBe n * n transmitting antenna correlation matrix, R
t=E (H
HH)/m
t=diag (α
1R
T, 1..., α
lR
T, l), R wherein
Tj, j=1 ..., l represents q
j* q
jJ bunch normalization transmitting antenna correlation matrix, α
jThen represent j bunch large scale decline information.Suppose R
T, jDifferent characteristic values is λ
J, k=1 ... K
j, promptly total number is K
j, λ
J, kTuple be τ
J, k,
R just
T, jOrder be t
j(1≤t
j≤ q
j).R
rBe that m * m receives correlation matrix, R
r=E{HH
H}/n, it is that a diagonal element is 1 complex symmetric matrix.Suppose R
rK different eigenvalue arranged
i, i=1 ... K, λ
iTuple be τ
i, satisfy
That is to say R
rOrder be m
1(1≤m
1≤ m).
Suppose set A
gComprise g bunch of antenna, corresponding large scale decline is α
1..., α
g, and set A
lComprise all l bunch antenna.For l bunch of antenna, always have 2
l-1 antenna set.Our purpose is exactly to select optimum set from all antenna set, and optimum distribution power.Suppose that a bunch inner constant power distributes, the power on each antenna is determined by power division matrix P, definition power allocation vector w=[w
1..., w
l], w
g, g=1 ..., l represents the g bunch of power weightings on the antenna, satisfies
Matrix P can be expressed as
Suppose that the power division weight is w
1..., w
l, can obtain STBC in the antenna set A
lReception noise η ratio during last the transmission is
h
t, t=1 ..., τ
J, kτ
i, representing independent identically distributed 0 mean variance is 1 multiple gaussian variable, η comprises the K ∑ as can be seen
J=1 lK
jThe individual independently degree of freedom is 2 τ
J, kτ
iCard side distribute with mechanism's variable
Its square generating function (MGF and characteristic function be not too big difference in form) can be write as
The MGF of η
η(s) then can be written as
In general,
η(s) write as and form be beneficial to further derivation more, but the power division weight also do not decide now, so we suppose a
jw
j, j=1 ..., l has nothing in common with each other. like this
η(s) can be written as
(4)
Coefficient q wherein
J, k, i, uThen can obtain by a set of equations,
(5)
By to
η(s) inverse transformation just can be obtained the probability density function f of η
η(x).
● the derivation of average SER expression formula and power allocation scheme
According to
η(s) (see formula (4)), utilize the relevant MQAM and the expression formula of MPSK STBC symbol in the mimo system of point-to-point of enclosed, document " Exact symbol error probability of orthogonalspace-time block codes " (In Proc.IEEE Globecom ' 02 referring to H.Shin and J.H.Lee, Taipei, Taiwan, 2002.1547~1552) formula (20) and formula (25) in), we can obtain STBC at (n, l, q
1..., q
l, the SER expression formula when m) transmitting MQAM and MPSK in the sub-clustering DWCS.
Each parameter is difficult to get information about to the influence of SER.Especially directly the power division weight that influences the STBC optimal transmission need obtain from the expression formula of optimizing SER, very big of difficulty.Yet we find, want the distribution power at the transmitting terminal optimum, only need from the characteristic value of transmission of receiving terminal feedback and reception correlation matrix just much of that.Arbitrarily selected A
gAs optimal set, and the positive optimum power w that assigns weight
1..., w
gCan obtain f
η(x) the upper bound, wherein
Bring in the approximate expression of SER,
Just obtained the upper bound of SER.
(8)
Wherein N is a set A
gThe mean value of the consecutive points number of corresponding STBC symbol constellation, d
gBe the minimum range of STBC unit energy planisphere,
The power division of suboptimum can be obtained by following optimization problem very easily.
Satisfy
By the Lagrangian method, obtain the power division weight of suboptimum
We find, the power allocation scheme of suboptimum is identical with suboptimum power allocation scheme based on outage probability, it is identical that is exactly that the order of the ratio of the power that distributes on every bunch of antenna and this bunch antenna transmission correlation matrix accounts for the ratio of whole cluster of antennas correlation matrix order sums, and and other parameters of system it doesn't matter.Obtain w
jAfter, carry it into formula (12) and (13), just obtain the SER of suboptimum.
Because A
gBeing arbitrary assumption, obviously may not be optimum.Given total transmitted data rates R and TSNR ρ are for the antenna set A
k, k=1 ..., 2
l-1, between each bunch,, obtain the SERP of corresponding suboptimum accordingly according to the distribution power of the order equal proportion of each bunch transmitting antenna correlation matrix
e Ak, the set of selecting to have minimum SER from all antenna set sends.So just can obtain the upper bound of optimum SER.
As shown in Figure 1, because each bunch spaced antenna spatially scatters, its spacing is far longer than signal wavelength, does not have correlation between spaced antenna.The antenna of each bunch inside and reception antenna are concentrated and are placed, and therefore may have correlation to a certain degree, and correlation is owing to less spacing or transmission environment between antenna causes.Because the user is possible different apart from length to the access of each spaced antenna, make that path attenuation differs greatly between each bunch, it is independent separately to add the shade large scale decline that different access path experiences, therefore, experienced different large scale declines (path fading, shadow fading) from the signal of each bunch spaced antenna transmitting-receiving.Transmitting terminal is according to carrying out the distribution of transmitted power from the transmission of receiving terminal feedback and the characteristic value of reception correlation matrix.The Space Time Coding device produces corresponding Space-Time Block Coding then, transmits above different cluster of antennas.All software realizations in central processing unit (CPU) of the generation of power division and Space-Time Block Coding.The present invention proposes following method.
Distribution method based on the downlink transmission power of average SER
As shown in Figure 2, concrete transmit power assignment algorithm is as follows:
● at first give parameter initialize, i=1, A=A
1, P=P
0=1.Wherein A is used to deposit optimum antenna set, and P deposits the SER of suboptimum.Initial set is A
1, initial SER is P
0
● receiving terminal is estimated the correlation matrix of transmission and reception antenna according to receiving pilot signal, and calculates characteristic value separately, and transmitting terminal obtains these characteristic values by feedback channel.
● transmitting terminal is according to the characteristic value from receiving terminal feedback, according to the distribution power of the order equal proportion of each bunch transmitting antenna correlation matrix, calculates A according to following formula between each bunch
iThe expression formula of SER when passing MQAM and MPSK symbol, (this antenna set comprises all cluster of antennas, for other set, only needs will gather in the corresponding cluster of antennas substitution following formula, and subscript j represents j bunch.Such as, if set A
iContain the 1st, 3,5 bunches, then in the summation of following formula, only need ask j=1,3,5 and)
(12)
(13)
Coefficient q
J, k, i, uFor
α wherein
jRepresent j bunch large scale decline information.λ
J, k, k=1 ... K
j, be the correlation matrix R of j bunch of transmitting antenna
T, jK
jIndividual different characteristic value, λ
J, kTuple be τ
J, k R just
T, jOrder be t
j(1≤t
j≤ q
j).λ
i, i=1 ... K is normalization reception antenna correlation matrix R
rK different characteristic value, λ
iTuple be τ
i, satisfy
That is to say R
rOrder be m
1(1≤m
1≤ m).
Beta, gamma, ζ are subscript.
Be the Appell hypergeometric function,
Be hypergeometric function, (a)
n=Γ (a+n)/Γ (a),
And
Be the Gamma function.
● travel through all antenna set, therefrom find out the set of minimum SER correspondence, this set is exactly optimum transmitting antenna set.
Fig. 3 has provided the power allocation scheme design sketch based on average SER.Consider the antenna structure of (4,2,2,2,2), data rate is 3bits/s.In this system, have three antenna set, set A
1(first bunch of antenna), 8PSK symbol, set A
2(first and second bunches of antennas), 16QAM symbol (3/4 speed), and set A
3(second bunch of antenna), the 8PSK symbol.For set A
2, we adopt second kind of power allocation scheme.As a comparison, set A
2Optimal performance also obtain by emulation by the power of adjusting two bunches of antennas, in the power adjustment process, may be on some TSNR level, second bunch of antenna may can not be utilized, but the constellation of 16QAM is keeping always.
Studied 1 simulated environment, u=[0.5,1], α
1=1, α
2=0.3.Because set A
3Performance not as A
1, so we just consider set A
1And A
2, it is optimum studying which set.Set A
1The SER performance, constant power distributes, set A under suboptimum power division and the optimal power allocation
2The SER performance.Performance as shown in Figure 3.
We find, the A of suboptimum power division
2The performance of performance and optimum is very approaching, even on lower TSNR level.The A that constant power distributes
2Performance then relative mistake some.This has proved the validity of the suboptimum power allocation scheme that we propose.According to our sky line options and power allocation scheme, optimum set will be at A
1Set A with the suboptimum power division
2Between compare generation.Should select A during less than 24dB as TSNR as can be seen
1, when TSNR is higher than 24dB, select A
2With compare two bunches of first-class power delivery of antenna, the antenna selecting plan that we propose has very big advantage, such as is 10 at SER
-2The time can reduce the TSNR of 2.5dB.
Although invention has been described with reference to accompanying drawing, it will be understood by those skilled in the art that can be under the situation that does not deviate from the aim of the present invention that is defined by the following claims and scope, and the present invention is carried out change on various forms and the details.